In one aspect, this invention relates to a supported, alkali metal fluoride-promoted palladium catalyst composition. In another aspect, this invention relates to a method of preparing this catalyst composition. In a further aspect, this invention relates to a process for selectively hydrogenating alkynes to alkenes, particularly acetylene to ethylene, in the presence of sulfur impurities employing the above-described catalyst composition.
The selective hydrogenation of alkynes, which frequently are present in small amounts in alkene-containing streams (e.g., acetylene contained in ethylene streams from thermal alkane crackers), is commercially carried out in the presence of supported palladium catalysts. In the case of the selective hydrogenation of acetylene to ethylene, preferably an alumina-supported palladium/silver catalyst in accordance with the disclosure in U.S. Pat. No. 4,404,124 and its division, U.S. Pat. No. 4,484,015, is used. The operating temperature for this hydrogenation process is selected such that essentially all acetylene is hydrogenated to ethylene (and thus removed from the feed stream) while only an insignificant amount of ethylene is hydrogenated to ethane (to minimize ethylene losses and to avoid a "runaway" reaction which is difficult to control, as has been pointed out in the above-identified patents).
It is generally known by those skilled in the art that sulfur impurities (such as H.sub.2 S, COS, CS.sub.2, mercaptans and organic sulfides and polysulfides) when present in alkyne-containing feeds can poison and deactivate these palladium-containing catalysts. The present invention is directed to an improved palladium-containing catalyst which is used for selectively hydrogenating alkynes to alkene, in particular of acetylene to ethylene, in the presence of sulfur-containing impurities.